feat(nix): Add comprehensive Nix pre-commit hooks

[aRustyDev]

Summary

This PR introduces a comprehensive set of pre-commit hooks for Nix development, providing validation, formatting, and linting capabilities for Nix files, flakes, darwin configurations, and home-manager setups.

New Hooks Added

Core Testing Hooks

1. nix-flake-check - Validates flake.nix files using nix flake check
2. nix-build-check - Tests Nix builds for both flakes and legacy expressions
3. nix-darwin-check - Validates nix-darwin configurations (Darwin-only)
4. nix-home-manager-check - Tests home-manager configurations

Code Quality Hooks

5. nix-fmt - Formats Nix files (supports nixpkgs-fmt, alejandra, nixfmt)
6. nix-lint - Lints Nix files using statix and optionally deadnix

Key Features

• ✅ Automatic tool installation if missing
• ✅ Support for both flakes and legacy Nix expressions
• ✅ Clear, actionable error messages
• ✅ Configurable behavior via environment variables
• ✅ Platform-aware (e.g., darwin-check only runs on macOS)
• ✅ Follows existing repository patterns and conventions

Configuration Examples

repos:
  - repo: https://github.com/aRustyDev/pre-commit-hooks
    rev: main
    hooks:
      - id: nix-fmt
        args: [--formatter=alejandra]
      - id: nix-lint
        args: [--with-deadnix]
      - id: nix-flake-check
      - id: nix-build-check

Testing

All hooks have been tested with sample Nix configurations included in tests/nix/fixtures/.

Closes Issues

• Closes feat(nix): Implement nix-flake-check hook #15 (nix-flake-check implementation)
• Closes feat(nix): Implement nix-build-check hook #16 (nix-build-check implementation)
• Closes feat(nix): Implement nix-darwin-check hook #17 (nix-darwin-check implementation)
• Closes feat(nix): Implement nix-home-manager-check hook #18 (nix-home-manager-check implementation)
• Closes feat(nix): Implement nix-fmt hook #19 (nix-fmt implementation)
• Closes feat(nix): Implement nix-lint hook #20 (nix-lint implementation)
• Closes feat(nix): Add Nix hooks to .pre-commit-hooks.yaml #21 (Update .pre-commit-hooks.yaml)

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